CVE-2026-11404 Cesanta Mongoose Out-of-Bounds Read in MG_TLS_BUILTIN ClientHello Session ID Parsing
A remote attacker can crash HTTPS, MQTTS, or WSS services by sending a crafted TLS ClientHello with an oversized session ID length.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-11404?
CVE-2026-11404 is a high-severity denial of service vulnerability in Cesanta Mongoose, published on 9 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Cesanta Mongoose before 7.22 contains an out-of-bounds read in the built-in TLS server function mg_tls_server_recv_hello(), which uses an attacker-controlled session_id_len byte from a TLS ClientHello as a buffer index without validating it against the length of received data. A remote, unauthenticated attacker can send a single crafted ClientHello with an oversized session id length to read past the receive buffer, crashing any HTTPS, MQTTS, or WSS service built on MG_TLS_BUILTIN.
Weakness: CWE-125
Which versions are affected by CVE-2026-11404?
How do I fix CVE-2026-11404?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-11404 being exploited?
There is no known exploitation of CVE-2026-11404 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-11404, GHSA-cvgj-gr8r-q762, JLSEC-2026-1257, UBUNTU-CVE-2026-11404.